AB-INITIO INVESTIGATION OF REACTION PATHWAYS FOR INTRAMOLECULAR CHARGE-TRANSFER IN DIMETHYLANILINO DERIVATIVES

Minimum-energy paths relevant for intramolecular charge transfer (ICT) in 4-(dimethylamino)benzonitrile (DMABN) and in 4-(dimethylamino)benz ethyne (DMABE) have been theoretically investigated. They are expected to characterize the ''twisted''-ICT (TICT) and the ''rehybridized''-I CT (RICT) photoprocesses. Reaction paths for the L-a and L-b states an d the RICT state have been determined at the CIS level. The energy pro files along the reaction paths have been calculated with the CIS, CASS CF, and CASPT2 electronic structure theory methods. It is concluded th at stabilization of the L-a state along the TICT reaction path is resp onsible for appearance of the CT emission in DMABN in polar solvents. The absence of CT fluorescence in DMABE in polar solvents is tentative ly attributed to fluorescence quenching by the RICT state.